Inverter vs. Generator Purchase

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.
But how large of a generator will I need if I'll ONLY be using it to recharge the inverter batteries?  Will the Honda EU2000 portable generator suffice (I believe it's 2000W)?  Does the generator size only matter with regards to how long it takes to recharge the inverter batteries?

If you are only charging batteries, a Honda eu1000i is usually plenty.  You merely need to provide power to your trailers converter/charger and it draws relatively little power, typically around 750 watts for a 50A charger.    On the other hand, some of the inverters you are considering come in versions that have built in 100A chargers. In that case, you would be exceeding the limits of a 1000 watt genset.  100A X 14VDC = 1400 watts of power and the actual draw would be slightly more due to power losses.

More than 2000 watts of inverter is a very hefty power consumption. If you really expect to use that much, you are going to need an equaly hefty size battery bank, probably 4-6 golf cart batteries.  That's a lot of space, weighht and expense for once-in-ahile boondocking..
 
Gary:

As I said earlier I tested an EU2000i last month and it was winding up pretty good to power our Freedom 2000 set at 10 amps input. I was considering a 1000i but am convinced it could only provide enough continuous output for the 5 amp setting and that would take quite awhile to top of the batteries.
 
I tested an EU2000i last month and it was winding up pretty good to power our Freedom 2000 set at 10 amps input.

Yeap, that's right. 10A X 120V =1200 watts, which is beyond the eu1000i's continuous load rating. That's why I included the note about  the 100A [output] chargers on large inverter/chargers. But the typical trailer inverter set-up will retain the existing converter/chager and add an inverter-only such as the Xantrex XPower 3000. The existing converter/charger will likely be a 50A model and require only 5-6 amps of input at peak load
 
As I said earlier I tested an EU2000i last month and it was winding up pretty good to power our Freedom 2000 set at 10 amps input. I was considering a 1000i but am convinced it could only provide enough continuous output for the 5 amp setting and that would take quite awhile to top of the batteries.
There's a 10:1 ratio between current at 12 volts vs. current at 120 volts.  Power = Voltage x Current (amps).  Like Gary said, 10 amps at 120 volts = 1200 watts.  At 12 volts, it takes 100 amps to make the same power (12 volts x 100 amps = 1200 watts).

This means if your charger is drawing 10 amps from the AC line, it is delivering 100 amps (or close to it) to your batteries.  This is a heck of a lot of current unless you have a very large battery bank.  Generally, you should not exceed a C/4 charging rate for best battery life.  This is the capacity of the battery bank in Amp-hours divided by 4.  A 100 amp-hour battery should not be charged at more than 25 amps, a 200 amp-hour battery bank can be charged at 50 amps, etc.

Batteries take a lot of current for a couple of minutes when you first begin charging, then the rate tapers off as the batteries gain a charge.  It might be possible to start your Xantrex at the 5 amp setting (50 amps peak into the batteries) then switch to the 10 amp setting (100 amps peak into the batteries) once the battery's charge rate starts tapering off.

 
Lou Schneider said:
There's a 10:1 ratio between current at 12 volts vs. current at 120 volts.  Power = Voltage x Current (amps).  Like Gary said, 10 amps at 120 volts = 1200 watts.  At 12 volts, it takes 100 amps to make the same power (12 volts x 100 amps = 1200 watts).

This means if your charger is drawing 10 amps from the AC line, it is delivering 100 amps (or close to it) to your batteries.  This is a heck of a lot of current unless you have a very large battery bank.  Generally, you should not exceed a C/4 charging rate for best battery life.  This is the capacity of the battery bank in Amp-hours divided by 4.  A 100 amp-hour battery should not be charged at more than 25 amps, a 200 amp-hour battery bank can be charged at 50 amps, etc.

Batteries take a lot of current for a couple of minutes when you first begin charging, then the rate tapers off as the batteries gain a charge.  It might be possible to start your Xantrex at the 5 amp setting (50 amps peak into the batteries) then switch to the 10 amp setting (100 amps peak into the batteries) once the battery's charge rate starts tapering off.



I had to start at 5 amps to keep the 2000i from tripping for about 15 minutes.
 
RV Roamer said:
But the typical trailer inverter set-up will retain the existing converter/chager and add an inverter-only such as the Xantrex XPower 3000. The existing converter/charger will likely be a 50A model and require only 5-6 amps of input at peak load

RVRoamer / Ned - According to RVRoamer's above statement, am I correct to assume that I'll be able to use my existing converter/charger to recharge the batteries of a Xantrex XPower 3000 inverter (or its pure sine wave equivalent)?? Does this mean that I don't really need to buy the 3-stage charger that Ned mentioned?? Is there any advantage to buying the 3-stage charger rather than using the existing converter/charger?

Thanks
Gary

-------------------------------------
Gary added later on - you can probably disregard the above question.? I just read another post where Ned and RVRoamer were discussing this issue.? The basic impression I got is the 3-stage inverter charger may still be useful with larger inverters since it's capability is better than the standard converter that comes with the trailer.? Please let me know if I'm mistaken.

By the way, is it best to buy the inverter as a factory installed option?? I believe NuWa only offers a 2000W inverter for roughly $2350 including two extra 12V batteries (they don't offer 6V batteries, not sure if that's a problem).? Also, I'm not sure if it's pure sine vs. modified sine.? I guessing I may find a better deal with an after-market inverter, but I'd need to hire someone to install it since I'm not comfortable doing that.? I worry enough that I'm going to toast the inverter or something else anyhow later on when I try to use it :eek:? While I'm at it, I'd like to splurge enough to get an inverter that's large enough (at least 2000W, maybe 3000W or so) so I don't have any regrets later and don't have to sweat my power consumption so much.
 
Buying factory installed or later is mostly a question of price and if the factory unit is what you need.  The factory installed price is about right for an inverter/charger plus batteries.  12V or 6V doesn't make much difference, but you will generally get a bit more capacity in 6V batteries in the same space.

You won't damage the inverter in use, if you overload it, it will either open the circuit breaker or shut itself down.  As for size, have you read the article in our library about sizing batteries and inverters?  It will give you the information you need to properly size the unit.
 
Generally, I'd be more than a little concerned about the amount of battery power necessary to drive such a large inverter.? Off the top of my head, I'd bet you would need over a thousand pounds of battery to run a 3000 w inverter at even half power for more than an hour.? Maybe there are others here with the experience to definitively answer the question.? For me, a small generator is a lot less weight to pull up the hills.
Art
Revised:  After looking around a bit, it may not be quite so bad....    4 6V golf cart batteries (exide) can give you 150A for 110 min.  That's almost two hours at 1800 Watts, and they weigh under 250 pounds.  If you have the capability to charge them at 50A, it would take 3 to 3 1/2 hours.
 
600+AH of battery is typicallly used for a 3000W inverter.  Those will run the inverter at full power for over an hour, but it's rare that an inverter is run at full power for long periods.  Weight is more like 400-450lbs.
 
There are no simple answers to "how big an inverter?" and "how many batteries?", especially when the person asking has no RVing expereince on which to base an estimate of power consumption when in use.  Generally speaking, though, King is right - it is impractical to carry enough batteries to  make an inverter a substitute for shore power or genset if you continue to use power in the same way/style as when to are connected.  Pulling a continuous 1500 watts from a battery bank means a continuous 125 amps @ 12 VDC. That rate would totally discharge a set of four Size 27 12V deep cycles in  2.5-3.0 hours and below the recommended 50% level in 2 hours.  But in practice - and with a bit of heed toward conservation - it is rare to consume power at that high a continuous rate. All depends on te user, though.

As for charging, a 3 stage charger is ideal, but hardly a necessity.  Todays two stage chargers have good  charge management controls and do a pretty decent job. And more and more trailers are coming with the excellent Progressive Dynamics or Iota chargers as standard equipment. And sometimes those come with the Charge Wizard (3 stage controller) feature or sometimes you have to add it afterwards (under $100).  Likewise charger size is not a huge issue, as long as it is not grossly undersized for the job.  You won't observe all that much diference between the total chage time on a 100 amp charger vs 60A. The main difference will be the amoung of charge done in the first 30-45 minutes or so, when the bulk chage stage is operating.  That can be of value when you can ony run the genset for 30-45 minutes to get some charge back on the batteries, but if you have a bit more time, or are hooking to shore power or driving (engine alternator does charging), the initial bulk rate of charge is of little significance [in my opinion].
 
Ned said:
As for size, have you read the article in our library about sizing batteries and inverters?? It will give you the information you need to properly size the unit.

Thanks all for the advice.  Yes, I read the section in the Library article titled "Calculating How Many Batteries You Need".  It is quite good.  The two things I didn't really understand about the battery sizing section was:

1) does the formula in the example only apply to 6V batteries, or both 6V and 12V batteries?

2) At the very end, the result was "=2 pairs of 6V batteries, or 4 12V batteries".  In either case, that sounds like four batteries to me.  I don't understand pros/cons of 6V versus 12V batteries.  NuWa only offers 12V batteries.  By the way, does this quantity of batteries include the 2 batteries that come with the coach to begin with?  Are those batteries installed in the same location as the inverter batteries?

It sounds like I should try to make do with a 2000W inverter, espec. since I'll need so many batteries for a 3000W.

Gary
 
1. The calculations apply to both 6V and 12V batteries.  2 6V batteries in series are the same as 1 12V battery.

2. That looks like a misprint, 4 6V batteries are the same as 2 12V batteries.  Generally, 2 6V batteries give more ampere-hours than the equivalent 12V battery for the same amount of space.  If you have 2 6V batteries in the coach, then you just add 2 more, if needed, in parallel with the existing ones.  What your options are depends on what is installed in the RV now.  If you have 2 6V batteries, then you would add 2 more, if the existing batteries are fairly new.  You don't want to mix old and new batteries.
 
Ned said:
That looks like a misprint, 4 6V batteries are the same as 2 12V batteries.

Actually, it's correct. It was written with T-105 style 12V deep cycle batteries in mind. They have a capacity of approx 105 amp hours, so you'd need 4 of them to give roughly the same capacity as 2 pairs of 6V golf cart batteries (a "pair" meaning 2 6V batteries connected in series).
 
Tom, ok that makes more sense.  We don't usually run into such small capacity 12V batteries.  The 6V T-105 has 220AH of capacity.
 
Ned said:
The 6V T-105 has 220AH of capacity.

Understood Ned. So it would make sense that a 12V deep cycle battery of the same dimensions would have a capacity of approx half of that (105-110 AH).
 
In talking about (4) 6 volt batteries vs. (4) 12 volt batteries, for the same amp-hour capacity the 6 volt array will have half as many individual cells as the 12 volt version.  Each cell will be twice as large, which means it's plate assemblies will be twice as large as the 12 volt version.  This is a very good thing for deep cycle use.  If you're talking about wet cells, going with the 6 volt batteries means half as many cells to keep topped off vs. having 12 volt batteries.

There are also half as many individual current paths in the 6 volt version (4 pairs of batteries = 2 current paths) vs 12 volts (4 discrete current paths).  Fewer paths mean there's less chance of the batteries becoming unbalanced, where the total amp-hour capacity is reduced because one or more batteries are doing the lion's share of the work while the rest loaf.  Even something as simple as a little bit of corrosion can cause parallel batteries to become unbalanced.
 
Back
Top Bottom